This application claims the priority of Japanese Patent Application No. 11-343793 filed on Dec. 2, 1999, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an auxiliary imaging lens which can capture an image while keeping substantially the same field of view area even when taking a picture in a screen having an aspect ratio of 4:3, for example, which is greater in height than a screen having an aspect ratio of 16:9, in a TV camera having an imaging surface with an aspect ratio of 16:9, for example.
2. Description of the Prior Art
While high-definition TV receivers have recently been coming into wider use, actual images having an aspect ratio of 4:3 are still in use as well. In a TV camera using a solid-state imaging device such as CCD, visual signals having a given aspect ratio can be produced when a part of its imaging area is electrically masked. Hence, there has been developed a switchable camera which uses a solid-state imaging device having an imaging area for 16:9 size screen, captures an image by using the whole imaging area when capturing an image for 16:9 size screen, and switches its signal processing such that both side portions in the imaging area of the solid-state imaging device are electrically masked by a predetermined width when capturing an image for 4:3 size screen.
When yielding an image for 16:9 size screen in the switchable camera switching its aspect ratio as mentioned above, a field of view such as the one shown in FIG. 7A is obtained. When an image for 4:3 size screen is to be obtained, however, a part of both right and left sides thereof cannot be held within the field of view as shown in FIG. 7B, whereby the horizontal range is greatly narrowed as compared with the field of view area in a conventional TV camera used for only 4:3 size screen (shown in FIG. 7D). Though the field of view areas in both screens can be adjusted so as to coincide with each other by a zooming operation, such an adjustment is impossible at wide-angle end positions. Also, while the TV camera can be moved away from the object at the time of capturing the image for 4:3 size screen, such an operation may be impossible in a narrow studio and the like.
Therefore, taking account of an extender usually provided in a lens apparatus, the assignee of the present invention has already proposed a configuration in which a lens for correcting the field of view area (ratio converter lens) is attached to the extender (Japanese Unexamined Patent Publication No. 8-94929).
When capturing an image for 16:9 size screen while a lens for correcting the field of view area is attached to an extender as such, the lens is disposed at a position shifted from the optical path. When capturing an image for 4:3 size screen, the extender is operated such that the lens for correcting the field of view area enters the optical path, thus making it possible to change the aspect ratio (see FIG. 7C).
Since the lens for correcting the field of view area is attached to the extender, it cannot easily be removed therefrom, whereby the lens for correcting the field of view area is used for only this TV camera, and it is difficult for the lens to be used in a plurality of TV cameras in common.
The lens for correcting the field of view area may be configured so as to be detachably mounted as an auxiliary lens between the main part of lenses and the camera body, instead of being attached to the extender. When such a lens is used, however, the exit pupil position approaches the imaging surface, thus shortening the eye point distance. As a consequence, upon color decomposition by use of a color-decomposing prism or the like, color shading may occur, thereby deteriorating the color reproducibility at marginal portions. Also, when an auxiliary lens is detachably mounted between the main part of lenses and the camera body, an operation of detaching the main part of lenses from the body in order to remove the auxiliary lens is necessary, whereby a lens having a better operability is desired in particular by cameramen who want to use such a lens in a handy manner in the outdoors.
Further, when capturing an image for 4:3 size screen with the main part of lenses suitable for capturing images for 16:9 size screen, it is necessary that the lens for correcting the field of view area have an afocal power of 0.8. Since so-called wide converter lenses which are commercially available include those having an afocal power of 0.8, they may be attached to the main part of lenses on the object side in place of the above-mentioned auxiliary lens device. As a consequence, the above-mentioned problem in the case of using the auxiliary lens device can be overcome.
However, if a commercially-available wide converter lens having an afocal power of 0.8 is thus used as it is, then a screen which originally necessitates an image circle with a diagonal length of 9 mm is required to secure an image circle with a diagonal length of 11 mm, which is inherent in the solid-state imaging screen, in order for the imaging lens itself to yield a wider angle of view. Therefore, it is necessary for the lens to have a larger outside diameter, which enhances its weight accordingly.
As a result, lenses become larger and heavier on the front side more than necessary. Since the body of TV camera has now been made lighter, the center of gravity will move forward if the front side is heavier, thereby becoming problematic in terms of balance.
As mentioned above, this kind of TV camera needs lightness and compactness since cameramen use it in a handy manner in the outdoors in particular. Also, the camera as a whole requires a favorable balance in order to make its imaging operation better. Therefore, those using a commercially-available wide converter lens mentioned above as it is may involve practically big problems therein.
For overcoming the problems mentioned above, it is an object of the present invention to provide an auxiliary imaging lens which can correct the field of view such that the color reproducibility can be attained in a favorable state when capturing an image for a normal size screen by using a TV camera for a horizontally longer size screen, can use the lens for correcting the field of view range in a plurality of TV cameras in common, and is excellent in lightness, compactness, and the balance of the camera as a whole.
The present invention provides an auxiliary imaging lens adapted to be attached to a main part of an imaging lens of a TV camera, the TV camera comprising a solid-state imaging device for capturing a horizontally longer size screen and being capable of capturing an image of a normal size screen by masking a part of right and left sides of the solid-state imaging device;
the auxiliary imaging lens being configured such that, when capturing the image for the normal size screen, an effective imaging area having such a size that the normal size screen in a case without using the auxiliary imaging lens is just held therein can be secured, and a focal length yielding a field of view area substantially on a par with a field of view area obtained when capturing the horizontally longer size screen can be set,
the auxiliary imaging lens being attachable to the main part of the imaging lens on the object side.
Here, xe2x80x9cnormal size screenxe2x80x9d mentioned above refers to one having a screen size with an aspect ratio which is commonly used in a conventional system, e.g., 4:3 size screen. On the other hand, xe2x80x9chorizontally longer size screenxe2x80x9d refers to one whose widthwise ratio is greater than the aspect ratio of the above-mentioned normal size screen and is, for example, 16:9 size screen.
The auxiliary imaging lens may comprise, successively from the object side, a biconcave lens and a biconvex lens.
The auxiliary imaging lens may be attached to the main part of the imaging lens by being screwed thereon or by means of a screw.
Also, the present invention provides an imaging apparatus comprising the auxiliary imaging lens.
In general, solid-state imaging devices include those with an aspect ratio of 4:3 conventionally used for cameras, those with an aspect ratio of 16:9 for wide cameras, and those for switchable cameras (in which 16:9 and 4:3 are switched therebetween).
In the case of ⅔-inch cameras, the imaging area has a diagonal length of 11 mm in each of the conventional cameras, wide cameras, and switchable cameras, whereas the width and height of its screen are 8.8 mmxc3x976.6 mm in the conventional cameras, 9.59 mmxc3x975.39 mm in the wide cameras, and 9.59 mmxc3x975.39 mm for 16:9 mode and 7.19 mmxc3x975.39 mm (with a diagonal length of 9 mm) for 4:3 mode in the switchable cameras.
When 4:3 mode is chosen in a switchable camera, only the area having a diameter of 9 mm is used in the imaging area having a diameter of 11 mm for 16:9 mode, so that the angle of view narrows by about 20%, whereby the viewing angle differs from that in the imaging area having a diameter of 11 mm taken in 4:3 mode for the conventional cameras. The resulting image on the screen cannot be considered to satisfy the original specs of the lens.
If an auxiliary imaging lens securing only an area having a diameter of 9 mm, which is the effective area for 4:3 mode, is attached to the front side of the main part of zoom lenses when a switchable lens is used in 4:3 mode, then its taking conditions (such as the field of view area) can be made substantially identical to those in an area having a diameter of 11 mm, which is the effective area of the conventional cameras used only for 4:3 mode, whereby the original specs of lens can be satisfied.
Also, it is smaller, lighter, and easier to handle, and can adapt to lenses incorporating no ratio converters, whereby the selectivity of lenses is widened.
Namely, since the auxiliary imaging lens of the present invention is configured such that a focal length yielding a field of view area substantially on a par with a field of view area obtained when capturing the horizontally longer size screen can be set when capturing an image for a normal size screen, a field of view area equivalent to that in the case of capturing an image for a screen having an aspect ratio of 16:9 can also be secured when capturing an image for a screen having an aspect ratio of 4:3, for example, whereby the part of image to be seen that is located on the right and left sides of the screen would not be cut.
Also, it is configured such that an effective imaging area having such a size that the normal size screen in a case without using the auxiliary imaging lens is just held therein can be secured when capturing the image for the normal size screen. As a consequence, when compared with the case where a commercially-available wide converter lens having an afocal power of 0.8 is attached as it is, the diameter can become about 80%, and the weight can become about the half, so that the lightness and compactness can greatly be advanced, and the TV camera as a whole can attain a better balance.
Further, when attaching/detaching the auxiliary imaging lens upon changing the imaging screen size, the main part of imaging lens can be left attached to the camera body, whereby operator""s operations for switching size screens can be improved.